Glutamate excitotoxicity has been implicated in loss of oligodendrocytes and their progenitors following ischemia and trauma and in demyelinating diseases. In particular, the progenitor stages of the lineage are most susceptible to many types of damage including excess glutamate. Studies both in vitro and in vivo have demonstrated that excess glutamate kills oligodendrocyte progenitors (OPs) via calcium influx through the AMPA/kainate receptors and that blockade of the AMPA/kainate receptors can protect oligodendrocyte progenitors from excess glutamate as well as from hypoxia-ischemia. Until recently, however, little was known about the mechanisms for glutamate-mediated toxicity. Our previous data demonstrated that excess glutamate leads to translocation of the pro-apoptotic Bcl family member Bax to the mitochondria, release of cytochrome c, activation of caspases 9 and 3 and death of oligodendrocyte progenitors. We also found that IGF-I has a unique ability to sustain activation of Akt and provide long-term protection of the oligodendrocyte progenitors from glutamate or trophic factor withdrawal, and that IGF-mediated survival in the presence of glutamate occurs downstream of calcium influx and upstream of Bax translocation and mitochondrial dysfunction. Thus, the goals of this proposal are to test the hypotheses that 1) glutamate toxicity of late OPs requires a Bax-mediated/mitochondrial pathway, which is activated through a calcium-induced cellular cascade, 2) IGF-I blocks Box-mediated mitochondrial dysfunction in OP cells through sustained IGF-IR/Akt signaling, and 3) perinatal H/I results in death of OPs through Box-mediated apoptosis, which can be blocked through activating Akt.